Calculate the spread after losses
The useful question is what it costs to deliver one kWh later. If charging costs 12p/kWh and AC-to-AC round-trip efficiency is 88%, the charging electricity for one delivered kWh costs about 13.64p. Avoiding a 28p import then creates an energy margin of about 14.36p per delivered kWh, before operating costs. Use prices on the same basis, with consistent VAT and tariff inclusions.
Use achievable operating days
A model that assumes a full cycle every day can overstate benefits. Your business may operate five days a week, have seasonal demand or close for maintenance. Battery availability, tariff windows and simultaneous solar generation also affect dispatch. Our calculator lets you set operating days and caps daily output by demand, power and charging time. Its presets are illustrative assumptions, not measured industry averages.
Get the whole installed cost
Separate the battery and inverter price from switchgear, cabling, civil works, fire strategy, communications, engineering, commissioning and grid connection work. Ask who owns each scope item. Include network reinforcement where required, and compare quotations on a consistent basis. The calculator uses the installed-cost figure you enter; it does not supply a verified market price.
Keep revenue streams separate
Energy shifting, reduced capacity charges, export, flexibility and trading revenues follow different rules and can compete for the same battery capacity. Do not simply add optimistic estimates together. Revenue can depend on dispatch rights, contracts, availability and the ability to meet service requirements. Our tool includes no export, flexibility revenue or demand-charge savings, and no assumption that a grid upgrade is avoided.
Read simple payback carefully
Simple payback divides installed cost by first-year net annual savings. It ignores finance, discounting, tax, replacement costs, residual value and changing prices. Our ten-year illustration reduces available battery output using your degradation assumption, but keeps other inputs fixed. It is a scenario, not a forecast or an investment recommendation. A non-positive net result has no positive simple payback under the entered assumptions.
Sources & further reading
Use current documents and confirm the requirements with your own network operator.
Created by Arcgrid. Educational information for commercial sites in Great Britain, not an engineering design or a guarantee of savings. Scenarios are illustrative. Northern Ireland has different connection arrangements.
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